Moves callbacks from being private functions of SoXt to belong to SoXtP, to remove some clutter from the generic SoGui.h file.
Moves callbacks from being private functions of SoXt to belong to
SoXtP, to remove some clutter from the generic SoGui.h file.

Misc codestyle fixes.

Alexpux/SoXt,Alexpux/SoXt,Alexpux/SoXt,Alexpux/SoXt